[braddo88]

Hi all,

Was thinking of making a hi-pass filter to sit between my pre and power however my input impedance is 470kohm - can anyone advise on cap size to roll off between 50-60Hz?

Thanks!

[richidoo]

https://www.omnicalculator.com/physics/high-pass-filter

50Hz = 6.7pF
60Hz = 5.6pF

It's hard to find high quality audio caps that small. Typical ceramic caps cheap to try, but treble quality might be compromised. Maybe this, but sometimes silver is too bright.

If you add a shunt resistor after the cap to lower the filter load impedance then you can use a normal size uF cap.
If your preamp output impedance is <1kOhm and can drive 13000 ohm load then try this A 13kOhm shunt resistor lets a standard 0.22 uF cap roll off at 55Hz. Since you have active preamp driving the 13000 resistor there should be no problem. If your preamp has very high output impedance then you can raise the shunt resistor to 47000 and use 56nF cap.

I think a shunt resistor with nice audiophile film cap is going to sound better than a tiny pF ceramic cap without the resistor. YMMV

[braddo88]

Thanks for the detailed response - appreciated.

My pre-amp specs:

- Freq: 0.1-200k Hz -1dB, 100kΩ
- Sensitivity: 150mVrms @0.5Vrms
- Input Impedance: 100 kΩ
- Output Impedance: < 300 Ω
- Power Consumption: 16 W
- Valve compliment: 3 x ECC83
- Dimensions (WDH): 405 x 270 x 70mm
- Weight: 3 kg

[Danny Richie]

We recently bought out a bunch of really small Gen.2 Sonicaps from .001 to .009 uF. So I may have just what you need.

You can see the values here: https://www.soniccraft.com/index.php/sonicap-gen-ii-c-301_49_51

[jmimac351]

We recently bought out a bunch of really small Gen.2 Sonicaps from .001 to .009 uF. So I may have just what you need.

You can see the values here: https://www.soniccraft.com/index.php/sonicap-gen-ii-c-301_49_51

Danny, I bought 2 different sets of these very small Gen II from you for making high pass for NX-Otica MTM.  I haven't played with them yet, but something I've wondered about... when you get into very small caps like this, in theory, is the smaller cap generally going to be "better / faster / cleaner"?  I've got some .0010uF and .0015uF Gen II for a 160Hz high pass and 100Hz high pass (for NX-Otica MTM).  My Ayre amps are 2Mohm input impedance, and are not capacitor coupled... frequency response is from DC, so the idea of putting a cap where it doesn't exist (on purpose) isn't super exciting, but then it occurred to me... there are several caps in my speaker crossovers too, might just have to get over it.  But I have a level of clarity now that is pretty special... I guess I just have to listen.

For 2 way speakers like NX-Studio and X-LS Encore, do you have an absolute favorite high pass frequency?  Those very small values allow for getting pretty granular with frequency selection, and I might as well have an ideal set for 2-ways, to try. 

[richidoo]

- Output Impedance: < 300 Ω

Excellent! You could drive a 5kOhm resistor if you wanted to.

So you can use 13kOhm resistor with 0.22uF cap if you have your heart set on an exotic audiophile cap that only comes in standard sizes.

Since Danny has smaller caps of good quality you can use 47kOhm shunt resistor with 0.056uF (=56nF) series cap, in case you get a different preamp in the future that would prefer the higher 47kOhm load resistance.

[Danny Richie]

Danny, I bought 2 different sets of these very small Gen II from you for making high pass for NX-Otica MTM.  I haven't played with them yet, but something I've wondered about... when you get into very small caps like this, in theory, is the smaller cap generally going to be "better / faster / cleaner"?  I've got some .0010uF and .0015uF Gen II for a 160Hz high pass and 100Hz high pass (for NX-Otica MTM).  My Ayre amps are 2Mohm input impedance, and are not capacitor coupled... frequency response is from DC, so the idea of putting a cap where it doesn't exist (on purpose) isn't super exciting, but then it occurred to me... there are several caps in my speaker crossovers too, might just have to get over it.  But I have a level of clarity now that is pretty special... I guess I just have to listen.

For 2 way speakers like NX-Studio and X-LS Encore, do you have an absolute favorite high pass frequency?  Those very small values allow for getting pretty granular with frequency selection, and I might as well have an ideal set for 2-ways, to try.

Give those caps a try and hear how they sound.

If it were me, I would shot for a number between 60Hz and 80Hz on the high side, and 50Hz to 70Hz on the low side.

[braddo88]

Excellent! You could drive a 5kOhm resistor if you wanted to.

So you can use 13kOhm resistor with 0.22uF cap if you have your heart set on an exotic audiophile cap that only comes in standard sizes.

Since Danny has smaller caps of good quality you can use 47kOhm shunt resistor with 0.056uF (=56nF) series cap, in case you get a different preamp in the future that would prefer the higher 47kOhm load resistance.

Thanks Richidoo!  Appreciate the assitance and nice to have options (don't plan on changing amp/preamp)